A brief recap of respiration is given and therefore an explanation of why we need glucose and oxygen. The process of breathing is described in detail, including the role of the diaphragm. Adaptations of the alveoli are described. The human circulatory system is then described, including the role of the heart, arteries, capillaries and veins.

First broadcast:
25 March 2003

Students could trace the journey of some oxygen molecules that are breathed in. Some will pass through the alveoli into the blood for respiration, while others flow straight out again in an out-breath.